Why I am being billed for a suspended service??

I have tried canceling with Telkom numerous times and no one ever responds. I had to stop payment to force them to cancel my internet, hence the suspension. Now Telkom is billing me since last year and I am not using their service - The router is disconnected. How can a Service Provider Bill you for a service no longer in use? There is no data usage on the router as its been disconnected for a few months now. Pathetic! How do I resolve this? Because contacting Telkom is not an option.